Ответ:
б) x²+6x=9
x²+6x-9=0
D=b²-4ac=36-4•1•(-9)=36+36=72
x1= -b+√D/2a= -6+6√2/2=-3+3√2
x2= -b-√D/2a= -6-6√2/2= -3-3√2
(2-x)(x+3x²)≥0
x(2-x)(1+3x)=0
x=0 x=2 x=-1/3
+ _ + _
-----------[-1/3]--------[0]----------[2]---------------
x∈(-∞;-1/3] U [0;2]
D=5
a₁=-4,8
S₁₅=n*(a₁+a₁₅)/2=15*(-4,8-4,8+5*14)/2=15*(-9,6+70)/2=(70*15-15*9,6)/2=35*15-15*4,8=15(35-4,8)=15*30,2=453