Giải câu 5 bài ôn tập chương 4: Giới hạn.
a. limx→2x+3x2+x+4=2+322+2+4=510=12
b. limx→−3x2+5x+6x2+3x=limx→−3(x+2)(x+3)x(x+3)=limx→−3x+2x=−3+2−3=−1−3=13
c. limx→4−2x−5x−4
Ta có:
limx→4−(2x−5)=3>0
limx→4−(x−4)=0
⇒limx→4−2x−5x−4=−∞
d. limx→+∞(−x3+x2−2x+1)=limx→+∞x3(−1+1x−2x2+1x3)=−∞
Vì limx→+∞(−1+1x−2x2+1x3)=−1
limx→+∞x3=+∞
e. limx→−∞x+33x−1=limx→−∞x(1+3x)x(3−1x)=limx→−∞1+3x3−1x=13
f. limx→−∞x2−2x+4−x3x−1
=limx→−∞|x|1−2x+4x2−x3x−1
=limx→−∞−x1−2x+4x2−xx(3−1x)
=limx→−∞x(−1−2x+4x2−1)x(3−1x)
=limx→−∞−1−2x+4x2−13−1x=−23.