<u>Given</u>:
Given that we need to prove the identity 
<u>Proof</u>:
Step 1: Factor out the common term sin x, we get;

Step 2: Using the identity 

Step 3: Reciprocating sec x, we get;

Step 4: Splitting the denominator, we have;

Simplifying, we get;

Thus, the identity is proved.
Answer:
36
Step-by-step explanation:
we know that the interior angles equal 180 and that the triangles are congruent so, 66 + 78 = 144 so then we have to subtract 180 - 144 and that gives us 36
Hope I helped :)
They are 1st one is vertical angles, second one is complementary
F=\dfrac{9}{5}C+32\\\\A.\\\dfrac{9}{5}C+32=F\ \ \ |-32\\\\\dfrac{9}{5}C=F-32\ \ \ |\cdot\dfrac{5}{9}\\\\C=\dfrac{5}{9}(F-32)
B.\\F=212\to C=\dfrac{5}{9}(212-32)=\dfrac{5}{9}\cdot180=100\\\\212^oF=100^oC
C.\\F=80\to C=\dfrac{5}{9}(80-32)=\dfrac{5}{9}\cdot48\approx26.7\\\\80^oF\approx26.7^oC
Hi,
The like terms are 2xy, -xy and (1/2)xy, since they have the same variables and powers.