Answer:
c
Step-by-step explanation:
if I understand this right, then the expression is
2×sqrt(28) - 5×sqrt(63)
let's look for squared factors in the numbers under the square roots.
28 = 4×7 (4 is a squared number)
63 = 9×7 (9 is a squared number)
so,
2×sqrt(4×7) - 5×sqrt(9×7) =
= 2×2×sqrt(7) - 5×3×sqrt(7) = 4×sqrt(7) - 15×sqrt(7) =
= (4 - 15)×sqrt(7) = -11×sqrt(7)
