If f(r+s)=f(r)+f(s)∀r,s∈R. Let m and n be integers. Then f(nm) is equal to
A
mn
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B
f(m)f(n)
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C
mnf(1)
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D
nmf(1)
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Solution
The correct option is Cmnf(1) Given, f(r+s)=f(r)+f(s) ⇒f(1+1+1+1...x times)=xf(1) Also, we can say that, f(m)=f(mn+mn+mn...n times)=nf(mn)...(1) f(m)=f(1+1+...m times)=mf(1)...(2) equating (1) and (2), we get, mf(1)=nf(mn) Thus, f(mn)=mnf(1)