Determine the missing number in the equation 13-2=12-?

For the equation to work, you have to have the same number on both sides of the equal sign

so to find ?, you can do:

13 - 2 = 12 - ?       Simplify

11 = 12 - ?       Subtract 12 on both sides

-1 = - ?     Multiply -1 on both sides

1 = ?

second option

step-by-step explanation:

the measures of a triangle equal 180. use that to find x.

2x+3x+4x=180

9x=180

9x/9=180/9

x=20

now you know x, you know angle a is 40°, angle b is 60°, angle c is 80°.

because angle a is 40°, the first option doesn't work.

because angle b is 60°, the second option does work.

when you add angle a and b, you get 100°. complementary means it equals 90°, so the third option doesn't work.

when you add angle a and c, you get 120°, which is not 100.