We are given:
f(x+y)=f(x)+f(y)+2xy
and
f(1)=3
We need to find:
f(5)
—
Step 1: Find Pattern
Put:
x=y=1
Then:
f(2)=f(1)+f(1)+2(1)(1)
f(2)=3+3+2
f(2)=8
—
Step 2: Find
Using:
f(3)=f(2+1)
f(3)=f(2)+f(1)+2(2)(1)
f(3)=8+3+4
f(3)=15
—
Step 3: Find
f(4)=f(3)+f(1)+2(3)(1)
f(4)=15+3+6
f(4)=24
—
Step 4: Find
f(5)=f(4)+f(1)+2(4)(1)
f(5)=24+3+8
f(5)=35
—
Final Answer
f(5)=35
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