if 2a+3b=7 & ab=2, find 4a² +9b²
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2a+3b=7
(2a+3b)^2=49
4a^2+9b^2+12ab=49
4a^2+9b^2+12(2)=49
4a^2+9b^2=49-24
4a^2+9b^2=25
therefore
4a^2+9b^2 = 25
banerjeehritama:
but one question brother, why is that 12 ab?
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