(6x-1)(1+6x)-14 < 7x(2+5x)
36x² - 1-14 < 14x+35x²
36x² - 35x² -14x -15 <0<br>x² -14x -15<0<br>x² -14x -15=0
D=14² - 4*(-15)=196 +60=256
x₁= 14 - 16 = -1
2
x₂ = 14+16 = 15
2
+ - +
-------- -1 ---------------- 15 --------------
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x∈(-1; 15)