JAMB 2002 · UME · Q2

Simplify $(\sqrt{0.7} + \sqrt{70})^2$ .

Worked solution (try it first)

Expand: $(a + b)^2 = a^2 + 2ab + b^2$ , so this is $0.7 + 2\sqrt{0.7 \times 70} + 70$ .
$0.7 \times 70 = 49$ , so the middle term is $2\sqrt{49} = 14$ .
Add: $0.7 + 14 + 70 = 84.7$ , option C.