7*9 = (7*10) - (7*▲)

What is the value of ▲ in the equation?

7x9 = (7x10) - (7xa)

63=70-7a

-7=-7a

a (triangle) = 1

Can't type thta trignale thingie so subsitute with x

7*9 = (7*10) - (7*x)

we can multipily what we know

7*9=7 times 9=63

7*10=7 times 10=70

now we have

63=70 - (7*x)

add (7*x) to both sides

(7*x) + 63=70

subtract 63 from boths ides

(7*x) = 7

divide both sides by 7

x=1

the answe ris traignle is equal to 1