B.
sin^2x + cos^2x =1
hence Sin^2x-1 = - cos^2x
Percent means parts out of 100
70%=70/100=7/10
7/10 of x=28
'of' means multiply
7/10 x=28
multiply both sides by 10/7 to get rid of fraciton
x=40
the number is 40
Answer:

<em>good luck, i hope this helps :)</em>
Answer: C
Step-by-step explanation:
x-3y=5, y=x-7 *solve it
the answer is (8,1)
so..
C. (8,1) is a solution to both equations so it is a solution to the system