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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
sec2xdx
=2usec2udu
=2ud(tanu)
=2utanu2tanudu
=2utanu2sinucosudu
=2utanu+21cosud(cosu)
=2utanu+2ln|cosu|+C
=2xtanx+2ln|cosx|+C

Everyday Math 每日數學 之 Statistics (Change of Data) #20190522 (+Solution)


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(2101π4)cscπ4cotπ4+cscπ4cos(2101π4)
=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
M2 (代數&微積分)
MC 技巧特訓
傳授必學砌數技巧
A1 A2 概念重構
深入教授微積分技術
拆解 Section B killer 題
fx3650P 輕鬆屈機

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Everyday Math 每日數學 之 Quadratic Equation and Graph 二次方程及圖像 #20190515 (+Solution)


Answer : D

2019年5月17日星期五

Everyday Math 每日數學 之 Integration #20190517 (+Solution)





(a)
ex=1t1
x=ln(t1)
dx=1t1dt
1e4x+e3xdx
=1(1t1)4+(1t1)31t1dt
=1(1t1)3+(1t1)2dt
=(t1)31+t1dt
=t33t2+3t1tdt
=13t3+32t23t+ln|t|+C
=13(1ex+1)3+32(1ex+1)23(1ex+1)+ln|1ex+1|+C

(b)

Let u=ex . Then du=exdx .
1u5+u4du
=1e5x+e4xexdx
=1e4x+e3xdx
=13(1ex+1)3+32(1ex+1)23(1ex+1)+ln|1ex+1|+C ( by (a) )
=13(1u+1)3+32(1u+1)23(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)23(1u+1)+ln|1u+1|]u=eu=1
=(e4+e3)113(1e+1)3+32(1e+1)23(1e+1)+ln(1e+1)+196ln2