Solution
Given : $$9x^2+16y^2=60$$ ------------(i)
and $$3x+4y=6$$
Squaring both sides, we get :
=> $$(3x+4y)^2=(6)^2$$
=> $$9x^2+16y^2+2(3x)(4y)=36$$
=> $$60+24xy=36$$ [Using (i)]
=> $$24xy=36-60=-24$$
=> $$xy=\frac{-24}{24}=-1$$
=> Ans - (A)
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