Question

The law of cosines is a^2+b^2-2abcosC=c^2. Find the value of 2abcosC.

Answer 1

Answer:

(D)$7=2abcosC$

Step-by-step explanation:

It is given from figure that c=1, a=2 and b=2, thus using the law of cosines, we get

$c^2=a^2+b^2-2abcosC$

Substituting the given values, we get

$(1)^2=(2)^2+(2)^2-2abcosC$

$1=4+4-2abcosC$

$1=8-2abcosC$

$1-8=-2abcosC$

$-7=-2abcosc$

$7=2abcosC$

Thus, the value of $2abcosC$ is $7$.

Hence, option (D) is correct.

Answer 2

2ab x cos (C) = 7 because

a^2 + b^2 - 2ab x cos(C) = c^2
2ab x cos(C) = a^2 + b^2 - c^2
2ab x cos(C) = 2^2 + 2^2 - 1^2
2ab x cos (C) = 7