Isn't 8.1 △ 4.2-0.3 △ 2.1 plus 3 / 7 equal to 19 / 14?

Isn't 8.1 △ 4.2-0.3 △ 2.1 plus 3 / 7 equal to 19 / 14?

=81/42-6/42+6/14=75/42+6/14=25/14+6/14=31/14

How much is four divided by nineteen
I'm in a hurry!

4 △ 19 = 4 / 19

"1-11" is only added 19 times

1+1+1+2+2+3+3+4+4+5+5+5+6+6+7+7+8+9+10+11

The price is 7.8 yuan. On this basis, plus 5 percent points, 7.8 times 1.05 is equal to 8.19, so how can I get 1.05? If I add 20 points

One point, also known as a percentage point, is 0.01, 1.05 = 1 + 0.05, and an increase of 20 points is 1 + 0.20

Is one meter equal to 100 centimeters?

Yes

27 / 100 meters is equivalent to 27 / 100 meters

That's right. It's 0.27m

One meter is equal to 100 cm. Is it approximate or accurate
-2 degrees centigrade is approximate number?
Is it approximate to weigh 38 kg?

Accurate
-Two degrees centigrade is approximate
A weight of 38 kg is similar

What is 19 out of 27 - (7 out of 9 + 6 out of 27)

Simple calculation:
19 of 27 - (7 of 9 + 6 of 27)
=19 of 27-6 of 27-7 of 9
=13 out of 27-21 out of 27
=-8 out of 27

If a + B = 3 and A-B = - 1, then A2 + B2=______ ．

∵ a + B = 3, A-B = - 1, ∵ A2 + 2Ab + B2 = 9, ①, a2-2ab + B2 = 1, ②, ① + ②, 2 (A2 + B2) = 9 + 1 = 10, ∵ A2 + B2 = 5

The known numbers are: 1, 34, 597, 16925 According to this rule, the nth number is expressed by algebraic expression______ ．

The nth number should be 2n − 1n2