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Why is ultrasound less dangerous than x-rays?
I believe it is because ultrasound uses sound waves whereas x-rays are a form of ionizing radiation. (Ionizing radiation is radiation with enough energy to remove electrons from their orbit around a nucleus.) However, with today's advances in x-ray protection X-rays are not generally harmful unless in excessive amounts. Medical radiation (for the average individual) accounts for only 11% of the irradiation received over our lifetime. There are tons of consumer products (exit signs and skin lotions, for example) that expose us to radiation. Not to mention the sun... Anyway, my point is that ultrasound is probably safer than X-rays. But it is also important to know that the type of diagnostic information produced by each is different and if your doctor recommends you get an xray, don't insult him by suggesting an ultrasound instead. :)
How many non-zero angles are formed in a fan of 17 rays?
136 * * * * * Actually there are 17*16 = 272 angles. Assuming the rays do not meet at 180 degrees, each pair of rays forms two angles: one less than 180 deg and one greater.
What is ultrasound?
Ultrasound is sound which has a frequency higher than that of audible sound.( like radar )ADDED: Not like radar. That uses radio waves, although sonar and radar principles are similar.
Is 8.7-0.26 greater or less than 8?
Less
How many non zero angles are formed in a fan of 30 rays with common angles?
Assuming none of the rays meet at 180 degrees, each pair of rays gives rise to two angles: one less than 180 deg and one greater. There can, therefore, be a maximum of 30*29 = 870 angles. (There are 435 unique pairs of rays: ab, ac, ad...bc, bd, be, etc.)
