Question

give me an explanation and solution to this question

Answer 1

May it helps you.
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Answer 2

p²+q²+r² = 20. ______(1)
pq+qr+rs = 15 ______(2)
multiplying eq (2) by 2
we get 2pq+2qr+2rs=30. _____(3)
adding equation (1) and (3) we get
p²+q²+r²+2pq+2qr+2rs = 50
(p+q+r)²=50
p+q+r=√50=5√2

Hence the answer D is correct