Question

calculati:
a) $4 \sqrt{90} - \sqrt{10} -(3 \sqrt{160} -5 \sqrt{40)}$
b)

Answer 1

$\displaystyle 4 \sqrt{90} - \sqrt{10} -(3 \sqrt{160} -5 \sqrt{40} )= \\ =4 \cdot 3 \sqrt{10} - \sqrt{10} -(3 \cdot 4 \sqrt{10} -5 \cdot 2 \sqrt{10} )= \\ =12 \sqrt{10} - \sqrt{10} -(12 \sqrt{10} -10 \sqrt{10} )= \\ =12 \sqrt{10} - \sqrt{10} -2 \sqrt{10}= \\ =11 \sqrt{10} -2 \sqrt{10}= \\ =9 \sqrt{10}$