Question 66

If $$9x^2+16y^2=60$$ and $$3x+4y=6$$, then the value of xy is

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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