jika a = 2x, b = 7y, dan c = 9z, maka tentukan nilai dari a. a+b+c b. 2a²+3b-c² c. 2a²+3(b+c)² d. a²b²c² : 2 (a-b)

a.
a+b+c = 2x + 7y + 9z

b.
2a^2 + 3b - c^2
= 2(2x)^2 + 3(7y) - (9z)^2
= 2(4x^2) + 21y - 81z^2
= 8x^2 + 21y - 81z^2

c)
2a^2 + 3(b + c)^2
= 2(2x)^2 + 3(7y + 9z)
= 2(4x^2) + 21y + 27z
= 8x^2 + 21y + 27z

d)
a^2b^2c^2 : 2(a - b)
= (2x)^2(7y)^2(9z)^2 : 2(2x - 7y)
= 4x^2 49y^2 81z^2 : (4x - 14y)