BC
sin A= -----
AB
BC=AB*sinA
BC=10*0,9=9
5) p² - 4q² = (p-2q)(p+2q)
6) -36a² + 12ab - b². Сначала разделим на -1:
-36a² + 12ab - b² / -1 = 36a² - 12ab + b² = (6a-b)² = (6a-b)(6a-b)
7) 8y³ - 125x³ = (2y-5x)(4y²+10yx+25x²)
8) 8ab - ax - pb + px = a(8b-x) - p(b-x)
9) x³ - 3x² + 2x - 6 = (x-3)(x²+2)
10) (a+6)² - 25 = (a+6)² - 5² = (a+6-5)(a+6+5) = (a+1)(a+11)
-2x²-5x+3≤0
2x²+5x-3≥0 D=25+24=49 √D=7
x1=1/4[-5+7]=1/2 x2=1/4[-5-7]=-3
------------- -3------------------- 1/2--------
+ - +
x∈(-∞;-3]∪[1/2;∞)