Question

Tính nhanh giá trị biểu thức

a. A=( x - 1 ).( x - 2 ).( x - 3 )...( x - 100 ) với x = 50

b.B= 13a+19b+4a-2b với a+b =100

 

Answer 1

`a, = (x-1)(x-2) ... (x-49)(x-50) ... (x-99)(x-100)`

`= (50-1)(50-2) ... (50-49)(50-50)...(50-99)(50-100)`

`= 0`.

`b, 13a + 19b + 4a - 2b`

`= 17a + 17b`

`= 17(a+b)`

`= 17 xx 100`

`= 1700`

Answer 2

a)

= (x - 1) (x - 2) ... (x - 49) (x - 50) ... (x - 99) (x - 100)

= (50 - 1) (50 - 2) ... (50 - 49) (50 - 50) ... (50 - 99) (50 - 100)

= 0

b)

= 17a + 17b

= 17(a + b)

= 1700

Answer 3

a,=(x−1)(x−2)...(x−49)(x−50)...(x−99)(x−100)a,=(x-1)(x-2)...(x-49)(x-50)...(x-99)(x-100)

=(50−1)(50−2)...(50−49)(50−50)...(50−99)(50−100)=(50-1)(50-2)...(50-49)(50-50)...(50-99)(50-100)

=0=0.

b,13a+19b+4a−2bb,13a+19b+4a-2b

=17a+17b=17a+17b

=17(a+b)=17(a+b)

=17×100=17×100

=1700