第23页

信息发布者：
具体数值
字母取值
C
B
4900
$-\frac{49}{2}$
11
解​$：(1) $​当​$a = \frac {1}{4}，b = - 1$​时，
​$a^2 - b^2 = (\frac {1}{4})^2 - (-1)^2 = \frac {1}{16} - 1 = -\frac {15}{16}$​
解​$：(2)$​当​$a = \frac {1}{4}，b = - 1$​时，
​$(a + b)(a - b)=(\frac {1}{4} - 1)(\frac {1}{4} + 1)=(-\frac {3}{4})×(\frac {5}{4})=-\frac {15}{16}$​
解​$：(3)$​当​$a = \frac {1}{4}，b = - 1$​时，
​$4a^2 - 4ab + b^2$​
​$ = 4×(\frac {1}{4})^2 - 4×\frac {1}{4}×(-1)+(-1)^2 $​
​$= 4×\frac {1}{16}+1 + 1$​
​$=\frac {1}{4}+2$​
​$=\frac {9}{4}$​
解​$：(4)$​当​$a = \frac {1}{4}，b = - 1$​时，
​$(2a - b)^2 = [2×\frac {1}{4}-(-1)]^2 = (\frac {1}{2}+1)^2 = (\frac {3}{2})^2=\frac {9}{4}$​
解​$：$​当​$x = 3，y = - 2$​时，
原式​$=\frac {3^3}{4×(-2)}-\frac {3}{(-2)^3}=-\frac {27}{8}-(-\frac {3}{8})=-\frac {27}{8}+\frac {3}{8}=-3$​
上一页 下一页