I actually posted this a while ago and it got answerd by a smart person so here's what I understood

the error is that it assumes that √(x²)=x
because if x is negative, it becomes positive
that's how the 2nd line is wrong
the 2nd line is the first wrong step

it goes from 4-9/2+9/2
so it goes from 4-4.5+4.5
notice the part under the parenthsees
√((4-4.5)²)
if we evaluate 4-4.5, we get -0.5
but by squaring it we get 0.5

-0.5+4.5=4, yes
but when we square it we get
0.5+4.5=5, that is how it works

5 0

2 years ago

Find the cosine of angle B.

Alexandra [31]

$\boxed { \text {Cosine Rule : } a^2 = b^2 + c^2 - 2bc \cos(A) }$

9² = 12² + 15² - 2 (12) (15) cos (B)

81 = 144 + 225 - 360 cos(B)

81 = 369 - 360 cos (B)

360 cos (B) = 369 - 81

360 cos (B) = 288

cos (B) = 0.8

Answer: Cosine B = 0.8

$\boxed { \text {Cosine Rule : } a^2 = b^2 + c^2 - 2bc \cos(A) }$

12² = 15² + 9² - 2 (15)(9) cos (A)

144 = 225 + 81 - 270 Cos A

144 = 306 - 270 Cos A

270 Cos A = 162

Cos A = 3/5 or 0.6

Answer: Cosine Angle A = 3/5

4 0

2 years ago