1) If 20 m of wire is available for fencing off a flower -bed in the form of a circular sector, then the maximum area ( in sq m) of the flower-bed is A) 12.5 B) 10 C) 25 D) 30 Answer: Option CExplanation: Total length = 2r+rθ =20 ⇒θ=20−2rr Now, area of flower-bed, A=12r2θ⇒A=12r2(20−2r)r ⇒A=10r−r2 ∴dAdr=10−2r For maxima or minima , put ∴dAdr=0 ∴10−2r=0⇒r=5 ∴Amax=12(5)2[20−2(5)5] =12×25×2=25sq.m