f(×+1) = f (×) +2× +2 dan f( 1 ) = 1 tentukan nilai dari f( 4 ) a. 11 b. 13 c. 16 e. 20 kalo bisa pake cara ya!

f(x+1) = f(x) + 2x + 2

x = 1
f(1+1)= f(1) + 2(1) + 2
f(2) = 1 + 2 + 2
f(2) = 5

x= 2
f(2+1) = f(2) + 2(2) + 2
f(3) = f(2) + 6
f(3) = 5 + 6
f(3) = 11

x = 3
f(3+1) = f(3) +2(3) + 2
f(4) = 11 + 6+ 2
f(4) = 19