Question

(7x+4)*(2,1-0,3x)=0. Как решить?​

Answer 1

$(7x+4)(2,1-0,3x)=0\\(7x+4)(\frac{21}{10}-\frac{3}{10}x)=0\\7x+4=0,\frac{21}{10}-\frac{3}{10}x=0\\x_{1}=-\frac{4}{7},x_{2}=7$

Answer 2

1 способ

$(7x+4)(2,1-0,3x)=0\\14,7x-2,1x^2+8,4-1,2x=0\\2,1x^2-13,5x-8,4=0\\21x-135x-84=0\\7x-45-28=0\\D=(-45)^2-4\times7\times(-28)=2809=53^2\\\\x_{_{1,2}}=\dfrac{45\pm53}{2\times7} = \bigg[ ^\bigg7 _{\bigg-\dfrac{4}{7} }$

2 способ

$(7x+4)\times(2,1-0,3x)=0\\7x+4=0\:\:\:\:\:2,1-0,3x=0\\x_1=-\dfrac{4}{7} \:\:\:\:\:x_2=7$