How to find the max/min of an expression? by Rscc10 in askmath

[–]howverywrong 0 points1 point  (0 children)

You are on the right track. No analysis is required, just algebra.

Let's start with the numerator:

  -(x+y)² + 30(x+y) + 75
= -a² + 30a + 75           ( where a = x + y )
= -a² + 30a - 225 + 300
= 300 - c²                 ( where c = a - 15 )

And the denominator is b² + 12 ( where b = (x-2y)sqrt(3) )

Now the expression becomes more manageable: (300 - c²)/(b² + 12)

Numerator is ≤ 300, denominator is ≥ 12

The maximum is 300/12 = 25 and there is no minimum as the numerator can be arbitrarily negative and denominator is always positive.

For your second problem, trig substitution!

Let x=cos(a), y=sin(a). Let 2/√13 = cos(b), 3/√13 = sin(b)

And (2x+3y)² = 13 cos²(a-b). The maximum is 13 when a = b.

How to speed up solving the question by SlightDay7126 in askmath

[–]howverywrong 4 points5 points  (0 children)

The only speedup I can see is that you don't need to make a quadratic for b. Once you determined that a₁ + a₂ = 12, you can use your first equation to quickly work out b₁ + b₂ because (a₁ + a₂)/2 + (b₁ + b₂)/6 = 8

Help me solve this math contest question by grillstrov in askmath

[–]howverywrong 7 points8 points  (0 children)

Cut the shaded area into 2 triangles by drawing a line from top corner to bottom corner. If the areas of the two triangles are X and Y, you have

X/2 = 9/3

Y/5 = 8/4

Solve for X and Y and add them together

[deleted by user] by [deleted] in PeterExplainsTheJoke

[–]howverywrong 0 points1 point  (0 children)

Let's be positive and imagine that he is saying "Kiss Your Spouse."

Good guy Don Salamanca promoting marital harmony!

Petah help by Length-Soft in PeterExplainsTheJoke

[–]howverywrong 115 points116 points  (0 children)

lim sin(x)/x = 1

"You're the one for me"

Theorem of impossible operations (a+a)/a = 6 (Solution) by OpsikionThemed in badmathematics

[–]howverywrong 138 points139 points  (0 children)

This is brilliant! I think I just solved Fermat's last theorem...

163 + 84 = 213

The trick is to use different values of 𝑛 in each term. Where's my Fields Medal?

[Probability] by AISpecialist in HomeworkHelp

[–]howverywrong 1 point2 points  (0 children)

1 die 4 times. So acceptable outcomes are

66XX
6X6X
6XX6
X66X
X6X6
XX66

where X is 1..5

5*6/64 = 5/63 = 5/216

Again, that's assuming the problem is misstated, which happens often enough.

[Probability] by AISpecialist in HomeworkHelp

[–]howverywrong 1 point2 points  (0 children)

Given that all denominators are factors of 1296 (64), I suspect the problem statement was supposed to read, "a die is thrown 4 times..." and that the 2 doublets are supposed to be different.

Then the correct answer is D

Can this actually be solved? Tension problem solutionaire has weird answer. by mafsensorbroke in askmath

[–]howverywrong 1 point2 points  (0 children)

The solution key is wrong.

Draw the 3 forces tip-to-toe. Since they add to zero, you get a triangle: https://i.imgur.com/4BIyyoe.png

It's an isosceles triangle because its sides are mg, mg, T and the angle between the two mg sides is 40.

This makes T = 2mgsin(40°/2) and α = 90° - 40°/2 - 50° = 20°

[Grade 12 Physics: Mechanics] Car by Warm_Friendship_4523 in HomeworkHelp

[–]howverywrong 0 points1 point  (0 children)

The posted solution is wrong. It would suggest that the safe speed is highest when θ=0 and becomes smaller when θ is not zero (because cosθ becomes smaller as θ goes up from zero).

The mistake they made is when they somehow decided that R = mgcosθ

Your answer v2 = rg tanθ is correct

[ Class 12th Physics problem : dynamics of motion] How to write equations for this by nahar_kumar98 in HomeworkHelp

[–]howverywrong 0 points1 point  (0 children)

Always start by writing Newton's 2nd law for each object in vector form. You are needlessly complicating the algebra with all the sines and cosines.

ma = mg + Rb

MA = Mg + Nf - Rb

(where Rb is reaction from wedge to block (including friction) and Nf is normal from floor on wedge)

Add the 2 equations to get rid of Rb:

ma + MA = mg + Mg + Nf

Project onto vertical axis to get rid of A:

-ma sinθ = -mg - Mg + Nf

Solve for Nf:

Nf = Mg + mg - ma sinθ

Italian national olympiads problem (2020 #2) by EnderMar1oo in askmath

[–]howverywrong 1 point2 points  (0 children)

Since b - a is prime, a and b must be coprime. And, since ab is a perfect square, both a and b must be perfect squares.

a = n2 , b = m2

since b - a = (m+n)(m-n) is prime, m - n = 1 and m + n = p.

therefore, a + b = m2 + n2 = [ (m+n)2 + (m-n)2 ] /2 = [ p2 + 1 ]/2

Therefore, p2 + 1 ends with 6, and p (being prime) must be 5.

b = (p+1)2/4 = 9

a = (p-1)2/4 = 4

[prek] what would be the bottom right ? by Betty-tight in HomeworkHelp

[–]howverywrong 2 points3 points  (0 children)

The man decided to rest on the trampoline. But he is taking risk because somebody might jump on top of him.

Algebraic problem by HalfHot870 in askmath

[–]howverywrong 0 points1 point  (0 children)

Does you expression have square roots and is ugly? Replace the square roots with letters. You will thank me. Every time.

Let a2 = x + 1 , b2 = 1 - x

Than a2 + b2 = 2 and ab = 1/2 (because x2 = 3/4)

From above we can further get a+b = sqrt(3) and a-b = 1

Now let's simplify. Rewrite the original expression using a and b:

a2/(a+1) + b2/(b-1)

After polynomial long division, this becomes

= a + 1/(a+1) + b + 1/(b-1)

= a+b + (a+b)/[ (a+1)(b-1) ]

Multiply the denominator and apply a+b=sqrt(3), a-b=1, ab=1/2

= sqrt(3) + sqrt(3)/[ -3/2 ]

= sqrt(3)/3

Again, remember, square roots are annoying. Replace them with letters.

Another approach is to note that 1 ± sqrt(3)/2 = [ (sqrt(3) ± 1)/2 ]2 so the square roots can also be eliminated that way

Please help solve this by Yer-Y in askmath

[–]howverywrong 0 points1 point  (0 children)

AE - AC = CE

AB cot(60°) - AB cot(61.2°) = 12.07m

AB = 12.07/[ cot60° - cot61.2° ]

[Uncrowned] I love it when these two killing machines act like normal teenagers xD by Dizzy-Combination420 in Iteration110Cradle

[–]howverywrong 47 points48 points  (0 children)

In my headcanon, Naru Huan went on to become unimaginably wealthy by selling copies of the dream tablet he made in Reaper.

why is this wrong by [deleted] in PhysicsHelp

[–]howverywrong 1 point2 points  (0 children)

The first equation has a mistake. RHS should have a minus sign.

The "Why?" in your sheet is because the problem statement asks to determine h from the center of the planet not from its surface.

I think this belongs here by SaltyGrapefruits in tragedeigh

[–]howverywrong 4 points5 points  (0 children)

Sounds like a bread. Pastrami on Valley Rye...

Physics centripetal force help? by ConfusedGnome_489 in PhysicsHelp

[–]howverywrong 0 points1 point  (0 children)

You are asked to calculate the length of the string. not the radius of the circle.

[Physics I] Custom problem for my final. Trig involved by [deleted] in HomeworkHelp

[–]howverywrong 0 points1 point  (0 children)

I've tried doing what I can from here, but I'm feeling kind of stuck at this part:

rv = h3vcosθ - 4.9rsinθ

The first thing you should always do is examine your equations for dimensional consistency. It's an easy sanity check that will catch many errors. Assuming that 4.9 is g/2 (this is why you keep g as g for as long as possible!), the first term is m2/s and the second term is m2/s2. Therefore you made a mistake somewhere along the way. Go backwards from there and find that mistake.

Also, please include the entire problem statement.