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اگر $a + b = 7$ اور $a - b = 3$، $a^2 - b^2$ کیا ہے؟

A$14$
B$10$
C$21$
D$28$
Answer & Solution
Correct answer: C. $21$
مربع شناخت کے فرق کا استعمال کریں $a^2 - b^2 = (a+b)(a-b) = 7 \times 3 = 21$۔
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