52ص21
تكتب كل عدد كتابة علمية
A = 851,7 X 0,0018 X 0,073
A = 8,517 X 10^2 X 1,8 X 10^-3 X 7,3 X 10^-2
A = 8,517 X 1,8 X 7,3 X 10^-3
A = 9 X 2 X 7 X10^-3
A =126 X10^-3

B = 0,05 X 1200 X 10^-3
B = 5 X 10^-2 X 1,2 X10^3 X10^-3
B = 5 X 1 X10^-2
B = 5 X 10^-2

C = 181,47 / 78,956
C = 1,8147 X 10^2 / 7,8956 X 10^1
C = 2 X 10 ^2 / 8 X 10^1
C = ( 2 : 8 ) X 10^1
C = 0,25 X 10^1
C = 2,5 X 10^-1 X 10^1
C = 3 X 10^0

64 p 22
S = 1/2 +1/6 +1/12 +1/20 + 1/30
S = 30/60 + 10/60 + 5/60 +3/60 + 2/60
S = 50/60
S = 5/6
2) A = 1/n – 1/ n + 1
A = n +1 /n(n+1) - n/n(n + 1)
A = 1 / n(n+1)
A(1) = 1/ 1(1+1) =1/2
A(2) = 1 /2(2+1) =1/6
A(3) = 1 /3(3+1) = 1/12
A(4) = 1/4(4+1) = 1/20
A(5) =1 /5(5+1) = 1/30

A(n) = 1/n – 1 /n+1
A(1) = 1 - 1/2
A(2) = 1/2 - 1/3
A (3) = 1/3 - 1/4
A(4) = 1/4 - 1/5
A (5) = 1/5 – 1/6
بالجمع نجد
A(1)+A(2) +A(3) +A(4) +A(5) = 1 - 1/6 =6/6 – 1/6 = 5/6
S = 1/2 +1/6 +1/12 +1/20 + 1/30
S = 1 – 5/6

80 ص23
80 p 23
EA =x
Sin 60° = AB/EC
AB = 4 sin 60° = 4 X√3 /2 = 2√3
P (aBC) = 3 CD = 3 X4 =12
P(ABCE) = AE +EC +CB + AB
= x +4 +2 +x + 2√3
2x + 6 + 2√3
2 x +6 + 2 √3 = 12
2 x = 12 – 6 - 2√3
2x = 6 - 2√3
x= 6/2 - 2√3/2
x= 3 - √3