English Assignment
English Assignment
Mathematics for Junior High School Grade VIII
Chapter I. Algebra
Page 37, number 2.
The sum of Dad's and Mom's ages
is 70 years. Mom is 2 years younger than Dad. Next year, double of Mom's age is
70 years. How old are they now?
Answer:
From the question, They can be
symbolic, Dad by x and Mom by y. So we
can get operation of algebraic expressions:
i.
x+y=70
ii.
x=y-2
iii.
2(x+1)=70
Then we can use the operation
algebraic to find the value of Dad's and
Mom's age. we can calculate first
operation(i) and second operation(ii). you can insert second operation to first
operation, y-2+y=70 and is equal to 2y=72,
so you can get the value of y is 36. then, to find the value of x you
can use the third operation(iii) but before it you must multiply 2 with (x+1)
and it can be equal to 2x=68, so the value of x is 34. from the result we can
conclude that:
the sum of Dad's(y) now is 36 years old and the sum of Mom's(x) now is 34
years old.
Chapter II. The Relation and Function
Page 76, number 13
A function of f
is stated by formula of f(x)=9-3x-x2 with domain {-2,-1,0,1,2} the
range of the function is…
a.
{-1,6,9,11,14}
b.
{-1,6,9,11}
c.
{-1,5,9,11,14}
d.
{-1,5,9,11}
Answer:
from the
problem you must find the range. so you can use the formula of f(x).You can
insert the domain to the formula of f(x).
f(x)=9-3x-x2
i.
f(-2)= 9-3.2-22 is equal to -1
ii.
f(-1)= 9-3(-1)-(-1)2 is equal to 11
iii.
f(0)= 9-3.0-(0)2is equal to 9
iv.
f(1)= 9-3.1-(1)2 is equal to 5
v.
f(2)= 9-3.2-(2)2 is equal to -1
so the range of
the function is {-1,5,9,11}(D)
Chapter IV. The System of Linear Equations in Two Variables
Page 130, number 1.
Ani and Budi are going shopping to
buy books and pencils in a bookstore. the price of books and pencils they
bought are shown in table below. Determine the price of each pencil and each
book.
|
Buyer
|
Book
|
Pencil
|
Price
|
|
Ani
|
2
|
3
|
Rp. 7.200
|
|
Budi
|
3
|
2
|
Rp. 7.800
|
From the table we can change the table value by system of linear
equation.
Answer
we can symbolic book
by p and pencil by q, so we can get the system linear equation
i.
2x+3y=7200
ii.
3x+2y=7800
to find the answer of the question you can choose to solve
the problem by substitution method or elimination method.
if you choose
substitution method you can change first operation(i) to be x=(7200-3y)/2. then
you insert the new x to second operation, 3 multiply by (7200-3y)/2+ 2y=
7800, and you can get the value of y is 1200. and then you can substitution the
value of y to second operation(ii), 3x+2.1200=7800, so the value of x is 1800.
but if you choose elimination method you must make x or y at
first and second operation it be same, and you subtract them. First, multiply
first operation by 3, and can be 6x+9y=216.000. and then you multiply second
operation by 2, and can be 6x+4y=156.000. then you subtract first and second,
because they have same value of x. and after you subtract the operation you can get the value of x is 1800 and the
value of y is 1200. other the substitution method or elimination method likes
nix method or another.
so the price of each book is 1800 and the price of each
pencil is 1200.
Chapter
VII. Polyhedral
Page 275, number 10.
Given a rectangular prism has length of 6
cm, width of 4 cm and height of 3 cm. the volume of the rectangular prism is….
a.
42 cm3
b.
52 cm3
c.
62 cm3
d.
72 cm3
72 cm3
Answer:
the formula of volume rectangular prism
is the best area multiply by height or l.w.h is equal to 6 x 4 x 3= 72 cm3(d)
Chapter V. Geometry
and Measurement
Page 154 number 4.
A hypotenuse of a right triangle is 8 cm long. if the length
of one of the leg is 5 cm, then the length of the other leg is….
a.
6,25 cm
b.
7,25 cm
c.
8,25 cm
d.
9,25 cm
to calculate this problem, you must choose Pythagoras
theorems,, from the problem we know that
A hypotenuse of a right triangle is 8 cm long and the length of one of
the leg is 5 cm. so the length of the
other leg is square root of a hypotenuse of a right triangle square minus the
length of one of the leg square, and it is equal to square root of 82-52,
is equal to square root of 39, or it is equal to 6,25 cm(A)
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