If b = a + cp and r = ab + \(\frac{1}{2}\)cp2, express b2 in terms of a, c, r.

A.

b2 = aV + 2cr

B.

b2 = ar + 2c2r

C.

b2 = a2 = \(\frac{1}{2}\) cr2

D.

b2 = \(\frac{1}{2}\)ar2 + c

E.

b2 = 2cr - a2

Correct answer is E

b = a + cp....(i)

r = ab + \(\frac{1}{2}\)cp2.....(ii)

expressing b2 in terms of a, c, r, we shall first eliminate p which should not appear in our answer from eqn, (i)

b - a = cp = \(\frac{b - a}{c}\)

sub. for p in eqn.(ii)

r = ab + \(\frac{1}{2}\)c\(\frac{(b - a)^2}{\frac{ab + b^2 - 2ab + a^2}{2c}}\)

2cr = 2ab + b2 - 2ab + a2

b2 = 2cr - a2