19)
write an expression for the nth term, an, for the arithmetic sequence:
4, 12, 26

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.

i think that you should ask google for the answer to that problem because if we don't know it google does

answer: translate the circles so they share a common center point and dilate circle y by a scale factor of 3.