1.5 times 6 + 3x = 2.8 to solve the equation Be quick!

1.5 times 6 + 3x = 2.8 to solve the equation Be quick!

1.5×6+3x=2.8
9+3x =2.8
3x=9-2.8
3x=6.2
x=31/15

7.8 times 3x = 3.6

7.8×3X=3.6
x=（）
I can't figure out the number. It can be expressed as 18 / 39

36 * (- 14.12) + 18 * (- 4.26) - 18 * 17.5 (simple calculation)

36*(-14.12)+18*(-4.26)—18*17.5
=18*(-28.24)+188(-4.26)-18*17.5
=18*(-28.24-4.26-17.5)
=18*(-50)
=-900

The factorization of ax ^ 2-bx ^ 2-bx + ax + 2b-2a must be adopted!

ax^2-bx^2-bx+ax+2b-2a
=x²(a-b)+x(a-b)-2(a-b)
=(a-b)(x²+x-2)
=(a-b)(x+2)(x-1)

One ninth minus one sixth minus one eighteenth multiplied by 36
Why don't I think I can figure it out?

（1/9-1/6-1/18）*36
=36*1/9-36*1/6-36*1/18
=4-6-2
=-4

Use 120 cm iron wire to make a cuboid frame. The ratio of length, width and height is 3:2:1. What is the length, width and height of the cuboid? What is the volume

The length of the cuboid is 120 △ 4 × 3 / (3 + 2 + 1) = 15 (CM)
The width is 120 △ 4 × 2 / (3 + 2 + 1) = 10 (CM)
Height 120 △ 4 × 1 / (3 + 2 + 1) = 5 (CM)
Volume: 15 × 10 × 5 = 750 (cm3)

What is the remainder of 48 ^ 51 divided by 7?

48 ^ 51 → 6 ^ 51 → 6 * 36 ^ 25 → 6 * 1 ^ 25 = 6 divided by 7, the rest is 6. I don't know if you can understand. The remainder above is the same, for example, the first to the second, 48 - (6 * 7) = 6. Do you understand?

Sequence {an} = (9N ^ 2-9n + 2) / (9N ^ 2-1) 1. Prove that an belongs to (0,1) 2 and has innumerable items in the interval (1 / 3,2 / 3),
If yes, how many? If not, why not

1. Proof: an = (9N ^ 2-9n + 2) / (9N ^ 2-1)
=(3n-1)(3n-2)/((3n+1)(3n-1))
=(3n-2)/(3n+1)
=1-3/(3n+1)
From an = 1-3 / (3N + 1), we can see that {an} is an increasing sequence
When n = 1, an = 1-3 / 4 = 1 / 4 > 0
Moreover, 3 / (3N + 1) > 0, that is, an = 1-3 / (3N + 1) 2 / 3
So, only A2 = 4 / 7 is in the interval (1 / 3,2 / 3)

One tenth plus three eighths plus two fifths is how much process is needed

Four fourths plus fifteen fourths plus sixteen fourths

The result of simplification (1 / 36-a ^ 2) / (1 / A ^ - 6a) is

(1/36-a^2)÷（1/a²-6a）
Original formula = [1 / (6 + a) (6-A)] / [1 / a (a-6)]
＝[1／（6＋a）（6－a）]×a（a－6）
＝－[a／（6＋a）]