11079

caunay hinh nhu lop 5 thi phai

dung ko

cai bai 5 cua sgk

bài này tui bó tayy chấm com

1)2.3^x-5=49=>2.3^x=54=>3^x=27=>x=3

2)3^x+1=26=>x+1=3=>x=2

3)5^x-2=1=>5^0=>x-2=0=>x=2

4)9^x-1=1=>9^0=x-1=0=>x=1

martial nha

Ta có : B=1.2.3.4+2.3.4.4+....+(n-1)n(n+1).4

= 1.2.3.4 + 2.3.4.(5-1) + 3.4.5.(6-2) + ... + (n-1)n(n+1)[(n+2)-(n-2)]

=1.2.3.4 +2.3.4.5 - 1.2.3.4 + 3.4.5.6 - 2.3.4.5 + .... + (n-1)n(n+1).(n+2) - (n-2).(n-1).n(n+1)

= ( 1.2.3.4 - 1.2.3.4 ) + ( 2.3.4.5 - 2.3.4.5 ) + .... + ( n-1).n.(n+1).(n+2)

= 0 + 0 + 0 + ... + ( n-1).n.(n+1).(n+2)

= ( n-1).n.(n+1).(n+2)

Vậy B = ( n-1).n.(n+1).(n+2)

nham 4950

11 , 6 : 3 = \(\frac{58}{15}\)

11.6 : 6= 1.93333333....=1.9(3)

15 x 19 - 0,15 -  X = 15

  285     - 0,15 - X = 15

    284,85        - X = 15

                        X = 284,85 - 15

                        X = 269,85