plz solve this tomorrow is my exam
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a bit wrong the answer is 64√5 but still thanks
apologies, the mistake is in the third line. the formula for x³-1/x³ is (x-1/x)³+3(x-1/x) not (x-1/x)³+(x-1/x)... thanks for pointing out the mistake
third step of the second photo graph
it has been found that x-1/x =√5 ...... now, 7x³+8x-7/x³-8/x = 7(x³-1/x³)+8(x-1/x) = 7[(x-1/x)³+3(x-1/x)]+8(x-1/x) ....... now, on putting x-1/x =√5 we get, ...... 7[(√5)³+3(√5)]+8(√5) = 7(5√5+3√5)+8√5 = 56√5+8√5 = 64√5
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