Question

(10-с)(9-с)
как млчя

Answer 1

C*c-19c-90
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Answer 2

$(10 - c) \times (9 - c) = 90 - 10c - 9c + {c}^{2} = 90 - 19c + {c}^{2} = {c}^{2} - 19c + 90$