Which of the following is correct?
1 + 1 should equal 2.
1 + 1 should equal to 2.
"equal" or "equal to"?
In maths, it's widely used the word equals.
Given the suggestions, 1 + 1 should be equal to 2 is the proper choice. Using equals is just 1 + 1 equals 2.
Now in maths, should is not used when we are sure about the result. After working long calculations and having in mind what's the expected result, we introduce should.
No preposition needed. "One plus one should equal two".
However, if equal is used as an adjective, "to" is needed. "One plus one should be equal to two."