作业帮一道英文数学题,请大家帮忙解答,一定要讲解呀!if b is an integer,and x^2+bx—30=0,which of the following cannot be the value of b?A.1 B.6 C.7 D.13 E.29
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一道英文数学题,请大家帮忙解答,一定要讲解呀!if b is an integer,and x^2+bx—30=0,which of the following cannot be the value of b?A.1 B.6 C.7 D.13 E.29
一道英文数学题,请大家帮忙解答,一定要讲解呀!
if b is an integer,and x^2+bx—30=0,which of the following cannot be the value of b?
A.1 B.6 C.7 D.13 E.29
一道英文数学题,请大家帮忙解答,一定要讲解呀!if b is an integer,and x^2+bx—30=0,which of the following cannot be the value of b?A.1 B.6 C.7 D.13 E.29
如果一个整数,且x^2+bx—30=0,下列那一个不是b的值.
将答案一个一个带入式子中：若b为1,则x解出来为-6或5.若b为6,则x为无理数.若b为7,则x为3或-10.当b为13或29时,x都有整数解,所以b不可能为6,答案选B
the statement of the problem is not complete, you should say x is an integer as well
now consider the decomposition of (-30),
the posible decompositions are
1*(-30) 2*(-15) 3*(-10) 5...
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the statement of the problem is not complete, you should say x is an integer as well
now consider the decomposition of (-30),
the posible decompositions are
1*(-30) 2*(-15) 3*(-10) 5*(-6) 6*(-5) 10*(-3) 15*(-2) 30*(-1)
by the relationship between roots ans coefficents
we have the posible value of b are
-29, -13, -7, -1, 1, 7, 13, 29
we obtain that b cannot be 6,
hence the answer is B
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这道题问意思的应该是
不可以让根号下b^2+120为整数的是
把5个数代入
发现只有b=6上面那个式子不是整数
所以选B