The answer reference of the first volume of the seventh grade mathematics textbook (1) Exercise 2. 1
1 、( 1)6a？ cm？
(2)80% one yuan
(3)vt kilometers
(4)[(a+x)b-ab]m？
2 、( 1)(t+5)℃
(2)3(x-y) kilometers or (3x-3y) kilometers.
(3)( 100-5x)
(4)(? r？ A-? r？ a)cm？
3. The following table:
4, (1) annual tree height increased by 5cm.
(2)( 100+5n) cm
5. There are (a+ 1) seats in the second row; There are (a+2) seats in the third row; The number of seats in N rows is (a+n-1); 20+ 19- 1=38 (pieces)
6. Solution: V=( 1/2a? -? r？ )h(cm？ ), when a=6cm, r=0.5cm, h=0.2cm, v? ( 1/2? 6? -3? 0.5? )? 0.2=3.45(cm？ )
7 、( 1)2n； (2)2n+ 1 or (2n- 1)
8. Solution: The total number of matches of the three teams is [3 (3-1)]/2 = 3; Four teams, the total number of games is [4 (4-1)]/2 = 6; Five teams, the total number of matches is [5 (5-1)]/2 =10; N teams, the total number of games is [n(n- 1)]/2.
9, solution: password L dp d jlou, decipher it? Keys? X-3, what does the password mean? I am a girl? (Note: The answer to this question is not unique, as long as it is reasonable. )
Seventh grade math textbook answer reference (2) Exercise 58 pages
1.( 1)2(a+b)； ab； 10; 6(2) 1/2(a+b)h； 15
2.( 1) 5x, the degree is1;
(2)x？ +3x+6, degree 2, term x? ，3x，6；
(3)x+2, the degree is 1, and the term is x, 2.
The seventh grade math textbook answer reference (3) Exercise page 65
1. Solution: (1)12x-20x = (12-20) x =-8x.
(2) x+7x-5x= ( 1+7-5)x=3x。
(3) -5a+0。 3a-2。 7a=(-5+0.3-2。 7)a= -7。 4a。
(4) 1/3y-2/3y+2y =( 1/3-2/3+2)y = 5/3y。
(5)-6ab+ba+8ab =(-6+ 1+8)ab = 3ab。
(6) 10y？ -0.5? =( 10-0.5)y？ =9.5y？ .
2. Solution: (1) 3a+2b-5a-b = (3-5) a+(2-1) b =-2a+b 。
When a =-2 and b = 1,
Original formula =-2? (-2)+ 1=5.
(2)3x-4x？ +7-3x+2x？ + 1
=(3-3)x+(2-4)x？ +7+ 1
=-2x？ +8.
When x=-3, the original formula =-2? (-3)? +8=- 18+8=- 10.
3. Solution: (1) 4x+5x = 9x. (2) 3x- 1/2x = 5/2x。