In the given figure
There is a triangle RST
∵ RU is perpendicular on ST and bisects it
∴ Triangle RST is an isosceles triangle
∴ RS = RT
∵ RS = 3x + 9 and RT = 7x + 17
Equate them
∵ 7x + 17 = 3x + 9
Subtract 3x from both sides
∴ 7x - 3x + 17 = 3x - 3x + 9
∴ 4x + 17 = 9
Subtract 17 from both sides
∵ 4x + 17 - 17 = 9 - 17
∴ 4x = -8
Divide both sides by 4 to find x
∴ x = -2
Now substitute x by -2 in the expression of RS to find its length
∵ RS = 3(-2) + 9
∴ RS = -6 + 9
∴ RS = 3
