x2 - x - 42 = 0
D = b2 - 4ac
D = 1 + 168 = 169 = 13^2
x1,2 = -b ± √D/2a
x1 = 1 + 13/2 = 14/2 = 7
x2 = 1 - 13/2 = - 12/2 = -6
Ответ: x1 = 7; x2 = -6
x2 - x - 42 =(x-7)(x+6)
А)62,5\% т.к 100:(50+30)=1.25*50=62,5\%
Б)37,5\% (остаток)
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А) 2x^2-7x-9<0
Решаю по дискриминанту
D=49-4*2*(-9)
D=121
x=-b+-корень из D/2a
x=7+-11/4
x1=7+11/4=18/4=4,5
x2=7-11/4=-4/4=-1
б)x^2>49
x>7 или -7