1. 计算$(-m^{3})^{2}$的结果为(
A.$m^{5}$
B.$-m^{5}$
C.$m^{6}$
D.$-m^{6}$
C
)A.$m^{5}$
B.$-m^{5}$
C.$m^{6}$
D.$-m^{6}$
答案:1.C
解析:
$(-m^{3})^{2}=(-1)^2 · (m^{3})^{2}=1 · m^{3×2}=m^{6}$,结果为选项C。
2. (2024·盐城改编)下列运算结果正确的是(
A.$(-a^{3})^{3}=-a^{6}$
B.$(a^{3})^{3}=a^{9}$
C.$a^{2}· a^{3}=a^{6}$
D.$(-a^{2})^{4}=-a^{8}$
B
)A.$(-a^{3})^{3}=-a^{6}$
B.$(a^{3})^{3}=a^{9}$
C.$a^{2}· a^{3}=a^{6}$
D.$(-a^{2})^{4}=-a^{8}$
答案:2.B
解析:
A.$(-a^{3})^{3}=-a^{9}$
B.$(a^{3})^{3}=a^{9}$
C.$a^{2}· a^{3}=a^{5}$
D.$(-a^{2})^{4}=a^{8}$
B
B.$(a^{3})^{3}=a^{9}$
C.$a^{2}· a^{3}=a^{5}$
D.$(-a^{2})^{4}=a^{8}$
B
3. 计算:$(10^{3})^{7}=$
$10^{21}$
;$[-(p - q)^{2}]^{5}=$$- (p - q)^{10}$
.答案:$3.10^{21} - (p - q)^{10}$
解析:
$(10^{3})^{7}=10^{3×7}=10^{21}$;$[-(p - q)^{2}]^{5}=-[(p - q)^{2}]^{5}=-(p - q)^{2×5}=-(p - q)^{10}$
4. 计算:
(1)$(-x)^{3}· (x^{5})^{2}· x$;
(2)$2(x^{3})^{4}-x^{4}· (x^{4})^{2}+x^{6}· (x^{3})^{2}$.
(1)$(-x)^{3}· (x^{5})^{2}· x$;
(2)$2(x^{3})^{4}-x^{4}· (x^{4})^{2}+x^{6}· (x^{3})^{2}$.
答案:$4.(1) -x^{14} (2) 2x^{12}$
解析:
(1)$(-x)^{3}· (x^{5})^{2}· x$
$=-x^{3}· x^{10}· x$
$=-x^{3+10+1}$
$=-x^{14}$
(2)$2(x^{3})^{4}-x^{4}· (x^{4})^{2}+x^{6}· (x^{3})^{2}$
$=2x^{12}-x^{4}· x^{8}+x^{6}· x^{6}$
$=2x^{12}-x^{12}+x^{12}$
$=2x^{12}$
$=-x^{3}· x^{10}· x$
$=-x^{3+10+1}$
$=-x^{14}$
(2)$2(x^{3})^{4}-x^{4}· (x^{4})^{2}+x^{6}· (x^{3})^{2}$
$=2x^{12}-x^{4}· x^{8}+x^{6}· x^{6}$
$=2x^{12}-x^{12}+x^{12}$
$=2x^{12}$
5. 若$(9^{2})^{n}=n^{8}$,则下列结论正确的是(
A.$n = 4$
B.$n = 2$
C.$n = 3$
D.无法确定$n$的值
B
)A.$n = 4$
B.$n = 2$
C.$n = 3$
D.无法确定$n$的值
答案:5.B
解析:
$(9^{2})^{n}=9^{2n}=(3^{2})^{2n}=3^{4n}$,$n^{8}=(n^{2})^{4}$,因为$(9^{2})^{n}=n^{8}$,所以$3^{4n}=(n^{2})^{4}$,则$3^{n}=n^{2}$。当$n=2$时,$3^{2}=9$,$2^{2}=4$,不相等;当$n=3$时,$3^{3}=27$,$3^{2}=9$,不相等;当$n=4$时,$3^{4}=81$,$4^{2}=16$,不相等。所以无法确定$n$的值。
1
1
6. (教材 P25 复习题第 12 题变式)若$3×9^{m}×27^{m}=3^{21}$,则$m$的值为(
A.3
B.4
C.5
D.6
B
)A.3
B.4
C.5
D.6
答案:6.B 解析:由题意,得$3 × (3^2)^m × (3^3)^m = 3^{21},$即$3 × 3^{2m} × 3^{3m} = 3^{21},$所以$3^{1 + 2m + 3m} = 3^{21},$所以1 + 2m + 3m = 21,解得m = 4.
7. (1)比较大小:$2^{30}$_________$3^{20}$(填“$>$”“$<$”或“$=$”);
(2)若$x = 3^{m}$,$y = 27^{m}+2$,则用含$x$的代数式表示$y$,得$y =$
(2)若$x = 3^{m}$,$y = 27^{m}+2$,则用含$x$的代数式表示$y$,得$y =$
$x^3 + 2$
.答案:7.(1) < 解析:因为$2^{30} = (2^3)^{10} = 8^{10},$$3^{20} = (3^2)^{10} = 9^{10},$且$8^{10} < 9^{10},$所以$2^{30} < 3^{20}.$
$(2) x^3 + 2 $解析:$y = (3^3)^m + 2 = (3^m)^3 + 2 = x^3 + 2.$
$(2) x^3 + 2 $解析:$y = (3^3)^m + 2 = (3^m)^3 + 2 = x^3 + 2.$
8. 已知$a^{x}· a^{y}=a^{4}$,$(a^{x})^{2}· (a^{x})^{y}· (a^{y})^{2}=a^{9}$.
(1)直接写出结果:$x + y =$
(2)求$xy$的值.
(1)直接写出结果:$x + y =$
4
;(2)求$xy$的值.
答案:8.(1) 4 (2) 因为$(a^x)^2 · (a^x)^y · (a^y)^2 = a^{2x + 2y + xy} = a^9,$所以2x + 2y + xy = 9,所以8 + xy = 9,所以xy = 1
解析:
(1) 4
(2) 因为$(a^{x})^{2}·(a^{x})^{y}·(a^{y})^{2}=a^{2x}·a^{xy}·a^{2y}=a^{2x + xy + 2y}=a^{9}$,所以$2x + 2y + xy = 9$。由(1)知$x + y = 4$,则$2(x + y) = 8$,所以$8 + xy = 9$,解得$xy = 1$。
(2) 因为$(a^{x})^{2}·(a^{x})^{y}·(a^{y})^{2}=a^{2x}·a^{xy}·a^{2y}=a^{2x + xy + 2y}=a^{9}$,所以$2x + 2y + xy = 9$。由(1)知$x + y = 4$,则$2(x + y) = 8$,所以$8 + xy = 9$,解得$xy = 1$。
9. (教材 P25 复习题第 13 题变式)已知$A = 2^{36}$,$B = 4^{27}$,$C = 8^{16}$,试比较$A$,$B$,$C$的大小.
答案:9.因为$A = 2^{36},$$B = (2^2)^{27} = 2^{54},$$C = (2^3)^{16} = 2^{48},$36 < 48 < 54,所以A < C < B
解析:
因为$A = 2^{36}$,$B = 4^{27}=(2^2)^{27}=2^{54}$,$C = 8^{16}=(2^3)^{16}=2^{48}$,$36 < 48 < 54$,所以$A < C < B$。