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જો $a + b = 7$ અને $a - b = 3$ હોય, તો $a^2 - b^2$ શું થાય?

A$14$
B$10$
C$21$
D$28$
Answer & Solution
Correct answer: C. $21$
પૂર્ણવર્ગ તફાવતના નિત્યસમ $a^2 - b^2 = (a+b)(a-b) = 7 \times 3 = 21$ નો ઉપયોગ કરો.
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