№ 27 2
a − b2 –? a −b а) a = 1, b = 2;
a 2 − b 2 12 − 22 1 − 4 3 = = = = 3 ; a + b = 1+ 2 = 3 ; a −b 1− 2 −1 1
б) a = 3, b = 1;
32 − 12 9 − 1 8 = = = 4 ; a + b = 3+1= 4 ; ; 3 −1 2 2 a 2 − b 2 1, 42 − 12 0,96 = = = 2, 4 , a + b =1,4 + 1 = 2,4; a−b 1, 4 − 1 0, 4
в) a = 1,4, b = 1; г) a = –3, b = 1;
9 −1 8 a 2 − b2 = = = −2 ; a + b = –3 + 1 = –2. −3 − 1 −4 a −b
№ 28
а) x=2, y=3;
2 ⋅ x2 − 2 ⋅ y 2 2 ⋅ 22 − 2 ⋅ 32 2 ⋅ 4 − 2 ⋅ 9 −10 = = = =2; −1 ⋅ 5 −5 ( x − y )( x + y ) ( 2 − 3)( 2 + 3)
32 12 9 2 2⋅ 2 − 2⋅ 2 − 1 2 ⋅ x2 − 2 ⋅ y 2 77 36 2 3 = = 2 9= =2; б) x=1,5, y= ; 11 7 3 1 3 1 3 ( x − y )( x + y ) ⎛ 18 77 ⎞⎛ ⎞ ⎜ − ⎟⎜ + ⎟ 6 ⋅ 6 ⎝ 2 3 ⎠⎝ 2 3 ⎠
в) x = –2, y = 0;
2 ⋅ x2 − 2 ⋅ y2 2 ⋅ −22 − 2 ⋅ 02 8 = = =2 ( x − y )( x + y ) ( −2 − 0 )( −2 + 0 ) 4
г) x = 1,3, y = –0,5; 2 ⋅ 1,32 − 2 ⋅ ( −0,5 ) 2 ⋅ x2 − 2 ⋅ y2 2 ⋅ 1,69 − 2 ⋅ 0, 25 2,88 = = = =2. 0,8 ⋅ 1,8 1, 44 ( x − y )( x + y ) (1,3 + 0,5 )(1,3 − 0,5) 2
№ 29 а) x = 7, y = 4; 5x – 3y = 5 · 7 – 3 · 4 = 35 – 12 = 23; б) x = 6,5, y = 2,1; 5x – 3y = 5 · 6,5 – 3 · 2,1 = 32,5 – 6,3 = 26,2; 2 5
2 3
в) x = 12 , y = 9 ; 5x – 3y = 5 · 12
2 2 – 3 · 9 ⋅ = 62 – 29 = 33; 5 3
г) x = 18, y = 7,4; 5x – 3y = 5 · 18 – 3 · 7,4 = 90 – 22,2 = 67,8. № 30 6a + 7b 6 ⋅ 20 + 7 ⋅ 12 120 + 84 204 = = = = 17 ; 3a − 4b 3 ⋅ 20 − 4 ⋅ 12 60 − 48 12 6a + 7b 6 ⋅ 2, 4 + 7 ⋅ 0,8 14, 4 + 5,6 20 = = = =5; б) a = 2,4, b = 0,8; 3a − 4b 3 ⋅ 2, 4 − 4 ⋅ 0,8 7, 2 − 3, 2 4 6a + 7b 6 ⋅ 10,8 + 7 ⋅ 6 64,8 + 42 106,8 5 = = = = 12 ; в) a = 10,8, b=6; 3a − 4b 3 ⋅ 10,8 − 4 ⋅ 6 32, 4 − 24 8, 4 7
а) a = 20, b = 12;
8