Question

-2/5 (15xla3 -10x)+4/7x(21xla2-7)

Answer 1

$\it -\dfrac{2}{5}(15x^3-10x) + \dfrac{4}{7}x(21x^2-7) = -\dfrac{2}{5}\cdot15x^3+\dfrac{2}{5}\cdot10x +\dfrac{4}{7}x\cdot21x^2-\dfrac{4}{7}x\cdot7=\\ \\ \\=-6x^3+4x+12x^3-4x=6x^3$

Answer 2

$- \frac{2}{5}( {15x}^{3} - 10x) + \frac{4}{7}x( {21x}^{2} - 7) = \\ \\ - \frac{2( {15x}^{3} - 10x) }{5} + \frac{4x( {21x}^{2} - 7) }{7} = \\ \\ - \frac{2 \times 5x( {3x}^{2} - 2) }{5} + \frac{4x \times 7( {3x}^{2} - 1) }{7} = \\ \\ - \frac{10x( {3x}^{2} - 2) }{5} + \frac{28( {3x}^{2} - 1) }{7} = \\ \\ - 2x( {3x}^{2} - 2) + 4x( {3x}^{2} - 1) = \\ \\ { - 6x}^{3} + 4x + {12x}^{3} - 4x = \\ \\ ( { - 6x}^{3} + {12x}^{3}) + (4x - 4x) = \\ \\ {6x}^{3}$