Question

In triangle ABC, what is the measure of A if a = 15, b = 10, and c = 7?

57.12°

72.15°

103.21°

122.88°

Answer 1

Can you formulate the right law of cosine?

Answer 2

-2abcos?

Answer 3

@Nnesha

Answer 4

no its a^2=b^2+c^2-2bc(cosa)

Answer 5

2(10)(7)(cos 15)?

Answer 6

149

Answer 7

I just know I did it wrong

Answer 8

too fast. You need to separate the cos(alpha) part.

Answer 9

I got 149 for b^2 and c^2

Answer 10

\[a^2 = b^2 + c^2 + b c \cos(\alpha)\]
separate the cos(alpha)

Answer 11

b^2+c^2 = 149 is true, but does not help you in any way.

Answer 12

:/

Answer 13

You need to separate the alpha:\[\cos(\alpha) = \frac{a^2-b^2-c^2}{bc}\]\[\alpha = \cos^{-1} \left( \frac{a^2-b^2-c^2}{bc}\right)\]
Try it on your own

Answer 14

\[\cos^{-1} (\frac{ 15^2-10^2-7^2 }{ 10(7)})\]

Answer 15

i GET 23.56

Answer 16

@Frouzen

Answer 17

@Nnesha