=9-7+5
=2+5
=7
2、 [√(-3+7)]+5
=(√4)+5
=2+5
=7
Operation sequence of mixed operation
When performing mixed operations, the numbers in parentheses are calculated first, and the parentheses are from small to large. If there is a power, calculate the power first, and then from high to low.
Without brackets, if there is only addition and subtraction, or only multiplication and division, then it is calculated from left to right.
Without brackets, if there are multiplication, division and addition and subtraction, multiply and divide first, then add and subtract. What we should pay attention to here is priority, and multiplication and division take precedence over addition and subtraction.
Main characteristics of mixed operation
Main properties of 1, addition and subtraction mixed operation
(1) In the mixed operation of addition and subtraction, the result is kept unchanged by changing the operation order. That is, a-b+c = a+c-b.
(2) A number plus the difference between two numbers is equal to the number plus the minuend in the difference, and then the minuend in the difference is subtracted. Namely: a+(b-0) =a+b-c
(3) The sum of one number minus two numbers equals the sum minus the addend in turn. That is a-(b+c) = a-b-c.
(4) A number minus the difference between two numbers is equal to this number minus the minuend in the difference, plus the minuend in the difference, that is, A-(b-c) = A-b+c.
2. The main properties of mixed operation of multiplication and division.
(1) In the mixed operation of multiplication and division, the result is kept unchanged by changing the operation order. That is, axb÷c=a÷cxb.
(2) The quotient of a number multiplied by two numbers can be multiplied by the dividend in the quotient and then divided by the division in the quotient. Namely: ax (b ÷ c) = axb ÷ c
(3) A number divided by the product of two numbers can be divided by the factors in the product in turn. Namely: a ÷ (bxc) = a ÷ b ÷ c.
(4) The quotient of a number divided by two numbers is equal to the number divided by the dividend in the quotient and then multiplied by the divisor in the quotient. Namely: a÷(b÷c)=a÷bxc.