If 2x + 3y = 13 and xy = 6, find the value of 8x3 + 21y3. -Maths 9th

If 2x + 3y = 13 and xy = 6, find the value of 8x3 + 21y3. -Maths 9th
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Answer :

2x +3y = 13-----(1) xy =6-----(2) 8x³ +27y³   = (2x)³ +(3y)³ = (2x+3y)³ - 3*2x*3y(2x+3y)  [using (a+b)³ = a³+b³+3ab(a+b)] = (13)³- 18 * 6 *13 [ using (1) and (2)] = 2197 - 1404 =793
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