3x+ 7y = 20 and xy= 4, the value of 9x^2 + 49y^2 is
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Answer:
Step-by-step explanation:
(3x+7y)=20
{squaring both sides}
(3x+7y)²=(20)²
(3x)²+(7y)²+2*3x*7y=400 {(a+b)²=a²+b²+2ab}
9x²+49y²+42xy=400
9x²+49y²+42*4=400
9x²+49y²+168=400
9x²+49y²=400-168
9x²+49y²=232
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