1.lim(x->0)(3x^2+6x)/sin(3x)
=lim(x->0)(3x^2+6x)'/sin(3x)'.....羅必達定理
=lim(x->0)(6x+6)/3cos(3x)
=6/3
=2
2.lim(x->0)5x^2/(sec^2(x)-1)
=lim(x->0)(5x^2)'/(tan^2(x))'
=lim(x->0)10x/2tan(x)sec^2(x)
=lim(x->0)(5xcos^3(x))'/sin(x)'
=lim(x->0)5(cos^3(x)-3xcos^2(x)sin(x))/cos(x)
=5(1-3*0)/1
=5
3.lim(x->-2)[√(13-x^2)-3]/(x+2)
=lim(x->-2)[√(13-x^2)-3]'/(x+2)'
=lim(x->-2)[-x/√(13-x^2)]/1
=-2/√(13-4)
=-2/3
4.lim(x->2)[1/(x+5)-1/(2x+3)]/(x-2)
=lim(x->2)[(2x+3-x-5)/(x+5)(2x+3)]/(x-2)
=lim(x->2)[(x-2)/(x+5)(2x+3)]/(x-2)
=lim(x->2)[1/(x+5)(2x+3)]
=1/7*7
=1/49
5.lim(x->π/4)(tan(x)-1)/(cos(x)-sin(x))
=lim(x->π/4)(tan(x)-1)'/(cos(x)-sin(x))'
=lim(x->π/4) sec^2(x)/(-sin(x)-cos(x))
=2/(-√2)
=-√2
6.lim(x->1)(|x+2|-|x-4|)/(1-x^2)
=lim(x->1)(|x+2|-|x-4|)'/(1-x^2)'
=lim(x->1)(|1|-|1|)/(-2x)
=0/(-2)
=0
7.lim(x->0)x^2*sin(1/x)
=lim(x->0)sin(1/x)/(1/x^2)
=lim(y->∞)sin(y)/y^2.....y=1/x
=(-1~1)/y^2.....-1<=sin(y)<=1
=0
8.lim(x->3)[√(3x-1)-√(2x+2)]/(x-3)
=lim(x->3)[√(3x-1)-√(2x+2)]'/(x-3)'
=lim(x->3)[3/2√(3x-1)-1/√(2x+2)]/1
=3/2√(3x-1)-1/√(2x+2)
=3/2√8-1/√8
=1/2√8
=1/4√2
=√2/8
9a.使用畢氏定理:
Q=atan(3/4) => cos(Q)=4/5.....ans
9b.使用畢氏定理:
A=asin(-12/13) => 3Q or 4Q
=> cos(A)=5/13(4Q) or -5/13(3Q)
10.ln[(x^4+3)^2/x^5*√(x^2+1)]
=ln[(x^4+3)^2]-ln[x^5*√(x^2+1)]
=2*ln(x^4+3)-ln(x^5)-ln(x^2+1)^0.5
=2*ln(x^4+3)-5*ln(x)-0.5*ln(x^2+1)
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