Răspuns:
[tex]7 \sqrt{20} = 7 \sqrt{ {2}^{2} \times 5 } = 7 \times 2 \sqrt{5} = 14 \sqrt{5} [/tex]
[tex]3 \sqrt{125} = 3 \sqrt{ {5}^{3} } = 3 \times 5 \sqrt{5} = 15 \sqrt{5} [/tex]
[tex]4 \sqrt{80} = 4 \sqrt{ {2}^{4} \times 5 } = 4 \times {2}^{2} \sqrt{5} = 16 \sqrt{5} [/tex]
[tex]14 \sqrt{5} + 15 \sqrt{5} - 16 \sqrt{5} = 13 \sqrt{5} [/tex]
