f.2 maths plz help

(1)Given the sum of the squares of consecutive integers from 1 to n is S=n(n+1)(2n+1)/6.
a) find 1^2+ 2^2+.......10^2.
=10(10+1)(2乘10+1)/6
=110乘21/6
=385

b)find 1^2+ 2^2+.......20^2.
=20(20+1)(2乘20+1)/6
=420乘41/6
=2870

c)find 11^2+12^2+.......20^2.
=1^2+ 2^2+.......20^2 - ^2+ 2^2+.......10^2.
=2870 - 385
=2485

(2)Make x the subject of each of the following formulae.
1. 2xy+3=2x-y　　[x]
y+3 = 2x - 2xy
y+3 = x(2 - 2y)
y+3 / 2 - 2y = x
y+3 / 2(1-y) = x
x = y+3 / 2(1-y)
ans:
　　y+3
x=_____
　　2(1-y)

　　3x+1　
2.y=____　　　　[x]
　　1-3x

y(1 - 3x) = 3x+1
y - 3xy = 3x+1
y - 1 = 3x+3xy
y - 1 = 3x(1+y)
y - 1 / 1+y = 3x
y - 1 / 3(1+y) = x
x = y - 1 / 3(1+y)
　　y-1
x=_____
　　3(y+1)

　　2x+3
3.y=____　　　　[x]
　　x-1

y(x - 1) = 2x+3
xy - y = 2x+3
xy - 2x = y+3
x(y - 2) = y+3
x = y+3 / y - 2
　　y+3
3.x=___
　　y-2

1)Given the sum of the squares of consecutive integers from 1 to n is S=n(n+1)(2n+1)/6.
a) find 1^2+ 2^2+.......10^2.
=10(10+1)(2乘10+1)/6
=110乘21/6
=385

b)find 1^2+ 2^2+.......20^2.
=20(20+1)(2乘20+1)/6
=420乘41/6
=2870

c)find 11^2+12^2+.......20^2.
=1^2+ 2^2+.......20^2 - ^2+ 2^2+.......10^2.
=2870 - 385
=2485



(2)Make x the subject of each of the following formulae.

1. 2xy+3=2x-y　　[x]
y+3 = 2x - 2xy

y+3 = x(2 - 2y)

y+3 / 2 - 2y = x

y+3 / 2(1-y) = x

x = y+3 / 2(1-y)

　　y+3
x=_____
　　2(1-y)



　　3x+1　
2.y=____　　　　[x]
　　1-3x
y(1 - 3x) = 3x+1

y - 3xy = 3x+1

y - 1 = 3x+3xy

y - 1 = 3x(1+y)

y - 1 / 1+y = 3x

y - 1 / 3(1+y) = x

x = y - 1 / 3(1+y)

　　y-1
x=_____
　　3(y+1)



　　2x+3
3.y=____　　　　[x]
　　x-1
y(x - 1) = 2x+3

xy - y = 2x+3

xy - 2x = y+3

x(y - 2) = y+3

x = y+3 / y - 2

　　y+3
x= ___
　　y-2


1a)385
1b)2870
1c)2485
2a) y+3
x= _____
　　 2(1-y)

2b) 　y-1
x=_____
　　 3(y+1)

2c) y+3
x= ___
　　 y-2

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