. Star question:
If f(1)=4 and f(x+y)=f(x)+f(y)+7xy+4,then f(2)+f(5)=?
Choose the most appropriate option
A) 125
B) 977
C) 289
D) 1077
E) 111

Rationale: let x = 1 and y = 1 f ( 1 + 1 ) = f ( 1 ) + f ( 1 ) + 7 x 1 x 1 + 4 ⇒ ⇒ f ( 2 ) = 19 let x = 2 and y = 2 f ( 2 + 2 ) = 19 + 19 + 7 x 2 x 2 + 4 ⇒ ⇒ f ( 4 ) = 70 let x = 1 and y = 4 f ( 1 + 4 ) = 4 + 70 + 28 + 4 = 106 f ( 2 ) + f ( 5 ) = 125 answer : a
Answer: A