A circle has its centre at (3, −4) and the straight line $3x-4y+5=0$ is a tangent to it. What is the radius of the circle?

A tangent touches the circle exactly once, so the radius equals the perpendicular distance from the centre to the line: |$3(3)-4(-4)+5$| / √$(3^2+(-4{)}^2)$ = |9 + 16 + 5| / 5 = 30/5 = 6 units. The trap 30 units stops at the numerator and never divides; 1.2 units divides by 25, forgetting that the denominator is the square ROOT of $3^2+4^2$; and 0.4 units comes from mishandling the double negative, reading $-4\times (-4)$ as −16 and getting |9 − 16 + 5| = 2 on top.