若关于x的一元二次方程kx2+2(k+1)x+k﹣1=0有两个实数根,则k的取值范围是 ▲ .
计算:51×49=_________.
(1)(3a-4b)()=9a2-16b2;(2)(4+2x)()=16-4x2; (3)(-7-x)()=49-x2;(4)(-a-3b)(-3b+a)=_______.
计算: (1)(a+1)(a-1)=_________;(3)(-a+1)(a+1)=________; (3)(-a+1)(a+1)=________;(4)(a+1)(-a-1)=_______.
用字母表示平方差公式为:___________.
计算:(3x-y)(x+2y)=________.