Fergus Sir Mathematics
2018 DSE | Mathematics (Compulsory) 5** | Mathematics (Algebra and Calculus) 5** | 專教數學CORE及M2 | 考試專家 | 技巧取勝
2019年6月1日星期六
Everyday Math 每日數學 之 Integration #20190529 (+solution)
Let u=√x
Then x=u2
dx=2udu
∫sec2√xdx
=∫2usec2udu
=∫2ud(tanu)
=2utanu−2∫tanudu
=2utanu−2∫sinucosudu
=2utanu+2∫1cosud(cosu)
=2utanu+2ln|cosu|+C
=2√xtan√x+2ln|cos√x|+C
Everyday Math 每日數學 之 Mathematical Induction + Trigonometry + Differentiation #20190601 (+Solution)
Solution:
(a)
For any non-negative integer n , denoted by P(n) the proposition that cosxcos(2x)cos(4x)...cos(2nx)=sin(2n+1x)2n+1sinx .
Note that cosx=2sinxcosx2sinx=sin(2x)2sinx .
P(0) is true.
Let k be a non-negative integer. Assume P(k) is true.
Therefore, cosxcos(2x)cos(4x)...cos(2kx)=sin(2k+1x)2k+1sinx .
Note that cosxcos(2x)cos(4x)...cos(2kx)cos(2k+1x)=sin(2k+1x)cos(2k+1x)2k+1sinx=sin(2k+2x)2k+2sinx
Therefore, P(k+1) is true.
By the principle of mathematical induction, for any non-negative integer n , cosxcos(2x)cos(4x)...cos(2nx)=sin(2n+1x)2n+1sinx
(b) ddx[12101sin(2101x)cscx]
=−12101sin(2101x)cscxcotx+12101cscxcos(2101x)⋅2101
=−12101sin(2101x)cscxcotx+cscxcos(2101x)
ddx|x=π412101sin(2101x)cscx
=−12101sin(2101⋅π4)cscπ4cotπ4+cscπ4cos(2101⋅π4)
=√2
2019年5月18日星期六
全新 Fergus Sir DSE 2020 / DSE 2021 數學 CORE / M2 備戰課程
數學 Core
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M2 (代數&微積分)
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MC 技巧特訓
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傳授必學砌數技巧
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A1 A2 概念重構
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深入教授微積分技術
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拆解 Section B killer 題
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fx3650P 輕鬆屈機
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培訓考試技巧,重建答題框架
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2019年5月17日星期五
Everyday Math 每日數學 之 Integration #20190517 (+Solution)
(a)
ex=1t−1
x=−ln(t−1)
dx=−1t−1dt
∫1e4x+e3xdx
=∫1(1t−1)4+(1t−1)3⋅−1t−1dt
=−∫1(1t−1)3+(1t−1)2dt
=−∫(t−1)31+t−1dt
=−∫t3−3t2+3t−1tdt
=−13t3+32t2−3t+ln|t|+C
=−13(1ex+1)3+32(1ex+1)2−3(1ex+1)+ln|1ex+1|+C
(b)
Let u=ex . Then du=exdx .
∫1u5+u4du
=∫1e5x+e4x⋅exdx
=∫1e4x+e3xdx
=−13(1ex+1)3+32(1ex+1)2−3(1ex+1)+ln|1ex+1|+C ( by (a) )
=−13(1u+1)3+32(1u+1)2−3(1u+1)+ln|1u+1|+C
(c)
∫e15u5+4u4(u5+u4)2du
=∫e1(5u4+4u3)u(u5+u4)2du
=∫u=eu=1u(u5+u4)2d(u5+u4)
=∫u=eu=1u(u5+u4)−2d(u5+u4)
=−∫u=eu=1ud(u5+u4)−1
=−[u(u5+u4)−1]u=eu=1+∫u=eu=1(u5+u4)−1du
=−[(u4+u3)−1]u=eu=1+[−13(1u+1)3+32(1u+1)2−3(1u+1)+ln|1u+1|]u=eu=1
=−(e4+e3)−1−13(1e+1)3+32(1e+1)2−3(1e+1)+ln(1e+1)+196−ln2
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