1. Tính 

\(\left(8\dfrac{9}{4}+\dfrac{2}{7}\right)-\left(-6-\dfrac{3}{7}+\dfrac{5}{4}\right)-\left(3+\dfrac{2}{4}-\dfrac{9}{7}\right)\)

3x^2 + 14x + 15
= 3x^2 + 9x + 5x + 15
= 3x(x + 3) + 5(x + 3)
= (x + 3)(3x + 5)

1. a) \(\dfrac{5}{3}+\dfrac{-2}{7}-\left(-1,2\right)\)

    b) \(0,25+\dfrac{3}{5}-\left(\dfrac{1}{8}-\dfrac{2}{5}+1\dfrac{1}{4}\right)\)

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