Question

Calculate cos 0 to two decimal places

Answer 1

For this case we have by definition of the Cosines Law that:

$7 ^ 2 = 10 ^ 2 + 8 ^ 2-2 (10) (8)$* cosΘ

$49 = 100 + 64-160$cosΘ

$49 = 164-160$cosΘ

$49-164 = -160$cosΘ

$-115 = -160$cosΘ

$115 = 160$cosΘ

cosΘ= $\frac {115} {160} = 0.71875$

Rounding off we have, 0.72

ANswer:

Option C

Answer 2

We can use the law of cosines as follows:

$7^2 = 8^2+10^2-2\cdot 8 \cdot 10 \cdot \cos(\theta)$

We can rewrite this equation as

$49 = 164-160 \cdot \cos(\theta) \iff 160 \cdot \cos(\theta) = 115 \iff \cos(\theta)=\dfrac{115}{160}\approx 0.72$