Why is 3 m + 4 (m + 12) and 7 m + 12 equal

14m+60

Step-by-step explanation:

=3m+4(m+12)+(7m+12)

removing bracket, we get

=3m+4m+12×4+7m+12

=3m+4m+7m+48+12

14m+60

the sum of all the angles in a triangle are equal to 180

so you can add   the 3 given angles together to equal 180:

5y + 2y + 2y = 180

or since all three angles have the same letter, combine the 3 angles to equal 180:

9y = 180

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.