The economic theory that posits that reducing the marginal rate of taxation will create a productive economy and that is opposed to keynesian theory is known as

The answer is "Supply-side economics".

Explanation:

When there is low tax rates, it boosts the growth in economy by giving individuals motivators to work, save, and contribute more, this economic theory is known as supply-side economics. A basic belief of this theory is that giving tax reductions to high-pay individuals produces more noteworthy economic advantages than giving tax breaks to low income people.

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answer; the above statement is (true);