1-ое: x^2=94-13 x^2=81 x1=корень(81) x2= -корень(81) x1=9 x2=-9 Ответ 9*(-9)= -81
2-ое: 14+(x-7):2=78 14+(x^2-2x(-7)+7^2)=78 14+x^2+14x+49=78 x^2+14x+63-78=0 x^2+14x-15=0 D= 196+4*15=256
X1= (-14+корень(256))/2 = (-14+16)/2=1
X2= (-14-корень(256))/2 = (-14-16)/2=-15
X² - y² + 15x + 15y = (x - y)*(x + y) + 15*(x + y) = (x + y)*( x - y + 15)
2/2si2acos2a-cos2a/sin2a=(1-cos²2a)/sin2acos2a=sin²2a/sin2acos2a=sin2a/cos2a=tg2a