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The units digit of a perfect square is 6. What are the possible values of the tens digit?

Respuesta :

1, 3, 5, 7, 9 are the possible digits for the tens digit. Notice they are all odd.

My reasoning:

When you multiply any 2 numbers together, the last digit of the result will be the last digit of the product of the original last digits (ex. 12*7 = 84:  7*2 = 14 : 4 is last digit)

The last TWO digits of the result will be the same as the last 2 digits of the product of just the last two digits. (ex, 1422*234 = 332,748:  22*48 = 748 : 48 are last two digits )

If is a perfect square ends in 6,  the last digit squared must end in 6 as well.

The only single digit numbers squared that end in 6 are:    4*4=16   and   6*6=36  

They are the only 2 so the number that is being squared must end in 4 or 6

Let the second last digit be X.  X can be any digit.

So the last 2 digits of our number that is being squared are either   X6   or    X4

That is, the last 2 digits of the number are either (10X+6)   or   (10X+4),

this will result in X always being an odd number.

The possible values of the tens digit given that the units digit of the perfect square is 6 are; 9, 7, 5, 3, or 1

The reason for the above possible tens digit values are as follows:

The perfect square square formula is presented as follows;

a² + 2·a·b + b² = (a + b)²

Let a in the above formula represent the tens part of the number and let b represent the units part, we have;

When b ≠ 0

a·b = a × b is a multiple of 10, that has 0 as its last digit

a² is a multiple of 10, having a last digit of 0

Therefore, the term that determines the non-zero value of units digit is .

The single digit numbers that when raised to the power of 2 gives a number with 6 as the units digits are 4 (4² = 16), and 6 (6² = 36)

Therefore, two number, tens = a and units = b, give a perfect square that has the unit digit of 6 only when b = 4 or 6

The possible value of the tens digit are;

0² + 2 × 0 × 4 + 10 = 10; The tens digit = 1

0² + 2 × 0 × 6 + 30 = 10; The tens digit = 3

10² + 2 × 10 × 4 + 10 = 190; The tens digit = 9

Therefore, the tens digit are given by adding 1 to multiples of 8 (2 × 4 = 8), or multiples of 12 (2 × 6 = 12), which are;

Multiples of 8: 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96

Multiples of 12: 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132, 144

Adding 1 to the above multiples of 8 and 12 gives the tens digit as either; 9, 7, 5, 3, or 1

The possible values of the tens digit are; 9, 7, 5, 3, or 1

Learn more about place values here:

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