Answer:
She shaded area?
12 x 10 = 120
6 x 7 = 42
42 divided by 2 = 21
Now we subtract both areas:
120 - 21 = 99 of the shaded region.
Solution: The missing reason in Step 8 is substitution of
.
Explanation:
The given steps are used to prove the formula for law of cosines.
From step 5 it is noticed that our equation is
..... (1)
From step 7 it is noticed that the value of
is
.
So by substituting
for
in equation (1) we get the equation of step 8, i.e.,

Hence, the missing reason in Step 8 is substitution of
.