MCQ
$\sqrt{14} \times\sqrt{21}$ is equal to
- ✓$7 \sqrt{6}$
- B$6 \sqrt{7}$
- C$5 \sqrt{7}$
- D$\sqrt{147}$
✓
Answer
Correct option: A.
$7 \sqrt{6}$
(a)
Using: $\sqrt{a} \times \sqrt{b}=\sqrt{a b}$, we obtain
$\sqrt{14} \times \sqrt{21}=\sqrt{14 \times 21}=\sqrt{7 \times 2 \times 7 \times 3}=\sqrt{7^2 \times 6}=\sqrt{7^2} \times \sqrt{6}=7 \sqrt{6}$
Using: $\sqrt{a} \times \sqrt{b}=\sqrt{a b}$, we obtain
$\sqrt{14} \times \sqrt{21}=\sqrt{14 \times 21}=\sqrt{7 \times 2 \times 7 \times 3}=\sqrt{7^2 \times 6}=\sqrt{7^2} \times \sqrt{6}=7 \sqrt{6}$
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