Loading [MathJax]/jax/output/HTML-CSS/jax.js
Home / Aptitude Tests / Further Mathematics / If Un = kn2 + p...
If Un = kn2 + pn, U1 = -1, U5 = 15, find the ...

If Un = kn2 + pn, U1 = -1, U5 = 15, find the values of k and p.

A.

k = -1, p = 2

B.

k = -1, p = -2

C.

k = 1, p = -2

D.

k = 1, p = 2

Correct answer is C

Un = kn2 + pn,

U1 = -1,

U5 = 15,

when n = 1
U1 = k(1)2+ p(1) = -1
k + p = -1 --------eqn1
when n = 5
U5 = k(5)2+ p(5) = 15
25k + 5p = 15 --------eqn2
multiply eqn1 by 5 and eqn2 by 1
5k + 5p = -5 -------eqn3
25k + 5p = 15 -------eqn4
eqn4 - eqn3
20k = 20
k = 1
sub for k in eqn1
1 + p = -1
p = -1 -1 = -2