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CUET
General Test
Quantitative Reasoning
Algebra
If x4 + x2y2 + y4 = 391,
x2 + xy + y2 = 23, then
find x2 - xy + y2 .
16
19
17
34
Formula → x4 + y4 + x2y2 = (x2 + y2 + xy) × (x2 + y2 - xy)
⇒ 391 = 23 × (x2 + y2 - xy)
⇒ x2 + y2 - xy = \(\frac{391}{23}\) = 17