Cosine is

which applies to a right triangle. I hope that helps you.
I gotchu.
<span>3x-9x+6=20-3x+4x
Combine like terms.
-6x+6=20+x
Bring x over to the left side.
-x -x
-7x+6=20
bring 6 to the right side.
-6 -6
-7x=14
Divide -7 on both sides to isolate x.
x= -2
CHECK
</span><span>3x-9x+6=20-3x+4x
-6(-2)+6=20+(-2)
18=18
ANSWER: x= -2</span>
28 books. 59(current books) - 31(past books) equals the amount of books Sandy bought, which is 28 books. Hope it helped
3 4/10 is my answer
please can i have a brainliest