TRUE or FALSE!

The law of cosines reduces to the Pythagorean theorem when the triangle is right.

**my answer: FALSE!
is that right? @terenzreignz :)

Question

TRUE or FALSE!

The law of cosines reduces to the Pythagorean theorem when the triangle is right.

**my answer: FALSE!
is that right? @terenzreignz :)

terenzreignz · Answer

What's the law of cosines?

$$\Large c^2 = a^2+b^2 -2ab \ \cos(C)$$

terenzreignz · Answer

So, if it's a right angle, then we have C = 90 degrees...
$$\Large c^2 = a^2+b^2-2ab \ \cos(90^o)$$

anonymous · Answer

yup haha thats it :P

terenzreignz · Answer

What's cos(90) = ?

anonymous · Answer

=0 ?

terenzreignz · Answer

That's right, so this part just cancels out...
$$\Large c^2 = a^2 + b^2 \cancel{-2ab \ \cos(90^o)}$$

Leaving you with...?

anonymous · Answer

pythagorean theorem! :) so this is actually TRUE! ahh i see :)

terenzreignz · Answer

haha

anonymous · Answer

pythagorean theorem! :) so this is actually TRUE! ahh i see :)